This invention relates to a heat pump control and in particular to a control system for regulating the operation of a heat pump employing dual compressors.
The term heat pump, as herein used refers to a reversible refrigeration system capable of delivering, on demand, either heating or cooling to an air conditioned region. In most smaller heat pump systems, a single compressor is employed. Control of the system is thus relatively simple and presents relatively few problems. However, in many larger heat pumps, two compressors are utilized with each compressor being arranged to pump refrigerant through an associated closed loop refrigeration circuit.
In heat pump systems using two compressors, it is the common practice to stage the operation of the compressors when the heat pump is in a cooling mode of operation whereby the compressors are brought into operation in sequence as the cooling load on the system increases. However, both compressors are normally operated when the system is providing heating to the air conditioned region without regard to the heating demands placed on the system. The operation of both compressors in the heating mode is carried out primarily to prevent the inadvertent cycling of one of the compressors when the system is undergoing a defrost cycle. As is well known in the art, starting one of the compressors when the indoor fan is off, as is typical during defrost, will force the system to operate under adverse conditions which could damage the system.
The continuous operation of both compressors to avoid the problems associated with defrosting, however, gives rise to other problems which, although not as dramatic, can also lead to the needless wasting of energy and eventual failure of the system.